I. Field of the Invention
This invention relates to methods of imparting non-stick properties to metal surfaces, particularly the surfaces of metal foils and sheets, and to the resulting non-stick products. More particularly, although not necessarily exclusively, the invention relates to methods of imparting non-stick properties to foils and sheets made of aluminum and aluminum alloys.
II. Background Art
Aluminum foil and sheet is used widely in packaging and food preparation applications. Non-stick properties are very desirable for such applications and foils or sheets having such properties are commercially available. For example, a foil of this type is sold under the brand name “Release” by Alcoa corporation, and this foil is produced by coating a hard metal foil with a suspension of a thermosetting polymer containing siloxane and a solvent, and then partially curing the polymer in an oven at a temperature sufficient to remove the solvent completely. The polymer becomes solid, thereby trapping the siloxane within the polymer (see U.S. Pat. No. 6,423,417 to Robbins which issued on Jul. 23, 2002). The partially-cured coated foil is then annealed to render the foil soft, to fully cure the polymer and to obtain “dead-fold” characteristics (the ability to be folded without spring-back). This method is expensive because the coating can be applied only at low speed due to the need to partially cure the polymer. Furthermore, two heat treatments are required, and the suspensions used as the initial coatings are expensive.
U.S. Pat. No. 2,978,098 which issued to Post on Apr. 4, 1961 describes a method of applying a silicone oil coating to aluminum foil. A foil in coil form is immersed in a solution of the oil in a volatile solvent, then removed from the solution and dried.
There is a need for an improved method of imparting a non-stick surface to aluminum foil, for example for greater economy and ease of preparation.